1. Field of the Disclosure
The present subject matter is generally directed to mobile drilling rig assemblies, and in particular, to a raisable substructure of a mobile drilling rig with a movable center floor to facilitate drilling rig mast assembly and drawworks installation.
2. Description of the Related Art
In many land-based oil and gas drilling operations, drilling rigs are delivered to an oilfield drilling site by transporting the various components of the drilling rig over roads and/or highways. Typically, the various drilling rig components are transported to a drilling site on one or more truck/trailer combinations, the number of which may depend on the size, weight, and complexity of the rig. Once at the drilling site, the drilling rig components are then assembled, and the drilling rig assembly is raised to an operating position so as to perform drilling operations. After the completion of drilling operations, the mobile drilling rig is then lowered, disassembled, loaded back onto truck/trailer combinations, and transported to a different oilfield drilling site for new drilling operations. Accordingly, the ease with which the various drilling rig components can be transported, assembled and disassembled, and raised and lowered can be a substantial factor in the drilling rig design, as well as the rig's overall operational capabilities and cost effectiveness.
As drilling rig technologies have progressed, the size and weight of mobile drilling rigs has significantly increased so as to meet the higher drilling load capabilities that are oftentimes required to drill deeper wells, particularly in more mature oilfield formations. For example, it is not uncommon for many land-based mobile drilling rigs to have a 1500-2000 HP capability, with hook load capacities of 1 million pounds or greater. Additionally, there are some even larger 3000 HP mobile drilling rigs in operation, with hook and/or rotary load capacities exceeding 1.5 million pounds.
However, as the capacity—and the overall size and weight—of mobile drilling rigs increases, the size and weight of many of the various components of the rig also proportionately increase, a situation that can sometimes contribute to an overall reduction in at least some of the “mobility” characteristics of the rig. For example, a typical drawworks for a 2000 HP mobile rig may weigh in the range of 80-100 thousand pounds, or even more. Furthermore, individual sections of a drilling rig mast may be 30-40 feet or more in length, and may weigh 20-80 thousand pounds. In many cases, such large and heavy components require the use of a suitably sized crane so as to lift and position the various drilling components during rig assembly. Accordingly, while each the various larger rig components may be “transportable” over roads and/or highways from one oilfield drilling site to another, the overall logistical considerations for using at least some higher capacity mobile drilling rigs, e.g., 1500 HP and greater, may need to include having a crane present at a given drilling site prior to the commencement of drilling operations in order to facilitate initial rig assembly. Furthermore, a crane must also be present after the completion of drilling operations so as to facilitate rig disassembly for transportation to other oilfield drilling sites. As may be appreciated, the requirement that a crane be used during these assembly/disassembly stages can have a significant impact on the overall cost of the drilling operation, as well as the amount of time that may be needed to perform the operations.
Accordingly, there is a need to develop and implement new designs and methods for facilitating the assembly of modern mobile drilling rigs having higher operating capacities without relying on the use of a conventional crane to facilitate the assembly and/or disassembly the rig. The following disclosure is directed to the design and use of mobile drilling rigs that address, or at least mitigate, at least some of the problems outlined above.